Conventionally, there has been proposed a so-called biting preventing bolt which when inserted obliquely into a female screw member of a nut or the like, it allows the bolt to be threaded smoothly into the female screw member without any biting by guiding its own posture with a guide portion formed on its shaft portion appropriately. Although ordinary bolts have a shaft portion having a substantially constant diameter, such a biting preventive bolt is provided with a small diameter or a tapered guide portion at the front end of the shaft portion so that when the guide portion comes into contact with the peripheral face of a screw hole in the female screw member, the posture of the bolt is guided properly. For example, the Patent Document 1 has disclosed a bolt in which a constant diameter column portion having a small diameter is formed at the front end of the shaft portion and complete ridge is formed on this constant diameter column portion, and further the outside diameter of the constant diameter column portion is almost equal to a minimum value of the inside diameter of the female screw. In cases of a bolt having such a structure, when the bolt is inserted obliquely into the female screw, the complete ridge of the constant diameter column portion can catch the ridge of the female screw, and if it is continued to be tightened as is, the screw portions can properly engage with each other along a lead. Patent document 1: Japanese Patent Application Laid-Open No.2000-18226